fairly new to photography but the next purchase I want is a flash for my D5100. Been looking at the Speedlight SB range but some are real pricey. Any good recommendations out there to get me going - if I like it, then perhaps can invest in a proper Speedlight etc. Ideally be good to have flexibility on all angles of the flash

Metz makes very good flashguns, that will work with the Nikon Speedlights if you acquire them in the future. I bought my wife the Metz flash that is roughly equivalent to the Nikon SB-700, and it works well on her D7000. Also, when used as a remote (slave) flash, our SU-800 will fire it reliably.

On my Canon cameras, I have been pleased with the performance of my Nissin Di-866 II Professional. This one is available in a version for Nikons.

Really, however, we both favor our SB-800 Speedlights, which I acquired as pre-owned merchandise, at some saving in cost compared to the then-current SB-900.

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Very very cheap in comparison to Nikon ones. You wont get TTL (only iTTL) but if you use Manual and have not used a flash gun before, you wont notice the difference.

For example, youngnuo 560 ii will cost you around 70 dollars. It is a great flash gun to start with. If you like it (flash photography in general), you can always upgrade to nikon ones (sb800 etc). You can also get yongnuo flash triggers for roughly 20-30 dollars and use the flash gun as a slave.

Many 3rd party brands won't offer iTTL or Nikon's CLS off camera shooting, so keep that in mind when purchasing.

You can pick up used SB-600s for less than $150, and even SB-800s can come pretty cheap. They're great flashes and offer all the features and power that you'll need. Even the SB-400 will give you quite a bit more control than your camera's pop-up flash, but it's limited in the sense that there's no horizontal tilt, off camera support, is limited in power, and because the size of the flash's area is so small you can expect relatively harsh lighting. However, they're cheap, lightweight, make a great fill in flash, have a pretty long battery life, and you'll have no trouble finding one used for under $100 or even $75. Keep in mind that it will be replaced in the next few months with a newer model, though.

I have the SB-700, and while it's a nice flash, it is pricey. The Nissin or Sunpak are great. Even the Yongnuos are good, although they lack in features they're pretty damn powerful for the price.